Implantable medical devices, such as orthopedic and dental prostheses, can be made more permanent if the interface between the existing bone and the device contains some natural bone growth to knit the two components together. Such ingrowth has advantages over the use of bone cement, both in terms of stability and permanency.
“Bioactive” coatings on implantable medical devices allow for the ingrowth of natural bone into and around the device, forming chemical bonds between the device and natural bone. Calcium-phosphate coatings have been prepared and have been shown to promote direct bone apposition.
There are a variety of approaches to prepare a bioactive ceramic coating on a substrate, for example electrophoresis, plasma spray method, and the so-called biomimetic method. Several of these approaches have their drawbacks, however. The electrophoresis method, although a low-temperature coating technique, results in a relatively low bond strength at the interface between the coating and the substrate. Therefore, a post-sintering step is usually necessary. The plasma spraying method does provide a relatively strong bond, however due to the high temperatures involved in this method, the hydroxyapatite coating decomposes during the coating process. The biomimetic method results in carbonated nano-crystalline apatite that is chemically bonded to a substrate through the process of immersing the substrate in an aqueous solution containing calcium, phosphate, and carbonate ions. Other ions, such as sodium, potassium, magnesium, chloride, sulfate, and silicate, may optionally be present in the solution.
The coatings achieved by previously disclosed methods, however, do not have a gradient structure.
There have been attempts to incorporate different proteins into the biomimetic apatite coatings by mixing the proteins with the biomimetic coating solutions. However, only up to forty-five percent of the protein in the solution could be incorporated into the coating using the biomimetic method.
There remains a need in the art for improved bioactive ceramic coatings in addition to processes to prepare such coatings. There also remains a need in the art to improve the protein incorporation efficiency into apatite coatings.